This invention relates to oil film dampers which find effective use as applied to high speed turbo machines, for example the turbine rotor and shaft of a hot gas turbine engine such as an aircraft gas turbine engine, for vibration damping, and more particularly to improved piston type sealing rings therefor. Hot gas turbine engines usually employ a shaft mounted turbine wheel or rotor with the shaft positioned and supported between spaced rolling element bearings. Vibration damping capacity of this kind of rotor system where rotor-shaft imbalance is present is limited and difficult to predict. As a consequence, resonant vibrations are not only potentially violent and destructive but also deleteriously affect various operational speeds of the turbine rotor. Unless there is adequate damping in the rotor system, resonant excitation of a critical speed at the operating condition of the engine, or in acceleration through the critical speed, can result in rotor vibration amplitudes of destructive levels.
For the above reasons it has become a practice to utilize squeeze film dampers in conjunction with the supporting rolling element bearings of hot gas turbine engines.
In general such a damper includes an arrangement in which a bearing support member, for example, the outer annular race of a rolling element bearing, may move transversely radially and orbitally in a closely confining annular chamber in the bearing or engine housing. Oil under pressure is introduced into a defined annular squeeze film space between the bearing support and an opposite chamber wall. The noted support motion acts to exert a compressive force on or squeeze the oil film to cause viscous flow of the oil and resistance to motion of the bearing support. Such dampers as described may utilize piston ring type seals for the squeeze film space at each side thereof. These piston ring seals are generally used in combination with an open oil dam or groove at the ends of the squeeze film space next adjacent a ring for better ring sealing but with a change in fluid pressure distribution in the damper and some resultant loss of effectiveness of the damper. Attempts to eliminate the oil dam or its adverse effects have continued without a fully satisfactory solution.